Method for refining molten metal

ABSTRACT

A METHOD FOR REFINING A MOLTEN METAL SUCH AS MOLTEN PIG IRON. THE MOLTEN METAL WHICH CONTAINS IMPURITIES IS POURED INTO A VESSEL SUCH AS A SUITABLE LADLE. A PURIFYING AGENT WHICH REACTS WITH THE MOLTEN METAL TO ELIMINATE AT LEAST PART OF THE IMPURITIES THEREOF IS ADDED TO THE MOLTEN METAL. THEN THE MOLTEN METAL TO WHICH THE PURIFYING AGENT HAS BEEN ADDED IS STIRRED ONLY IN THE REGION OF THE SURFACE OF THE MOLTEN METAL. THE ADDING OF THE PURIFYING AGENT TO THE MOLTEN METAL AND THE STIRRING THEREOF TAKES PLACE AFTER THE MOLTEN METAL HAS BEEN POURED INTO THE VESSEL DURING A PERIOD OF TIME WHEN PARTS OF THE BODY OF MOLTEN METAL WITHIN THE VESSSEL ARE STILL IN MOTION. IN THE CASE OF PIG IRON THIS PERIOD OF TIME HAS A DURATION OF AT LEAST ONE HOUR.

July 13, 1971 mro ANDO ETAL 3,592,629

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rip-n RYo ANDO ETAL 3,592,629

METHOD FOR REFINING IOLTEN METAL July 13, 1911 Filed July 25, 1967 5Sheets-Sheet a Fig 3 Fig 4 INVENTOR.

July 13, 1971 RYO ANDO EI'AL IBTHOD FOR REPINING IOLI'EN METAL 5Sheets-Shut I Filed July 25, 1967 Fig 5 Angle of Inclination Fig 6INVENTOR WW) Fu/(us m y 1971 RYO moo ET L METHOD FOR REFINING ULTENMETAL 5 Sheets-Sheet 5 Filed July 25, 1967 w 5 555 271; Fun;

Time(Min.)

Fig 10 Number of Stirring Rods 3. f 1 Number of Stlrrlng Rm] l 0 0 0 m 9w 1 m Depth of Immersion (Cm) 1 u FM'UJIIIMA, #4 K4 "FA 5 "CH! HildeUnited States Patent US. C]. 75-58 7 Claims ABSTRACT OF THE DISCLOSURE Amethod for refining a molten metal such as molten pig iron. The moltenmetal which contains impurities is poured into a vessel such as asuitable ladle. A purifying agent which reacts with the molten metal toeliminate at least part of the impurities thereof is added to the moltenmetal. Then the molten metal to which the purifying agent has been addedis stirred only in the region of the surface of the molten metal. Theadding of the purifying agent to the molten metal and the stirringthereof takes place after the molten metal has been poured into thevessel during a period of time when parts of the body of molten metalwithin the vessel are still in motion. In the case of pig iron thisperiod of time has a duration of at least one hour.

BACKGROUND OF THE INVENTION The present invention relates to therefining of molten metals.

In particular, the present invention is applicable to the refining ofmolten pig iron and is especially useful in desulfurizing and indephosphorizing the molten pig iron.

At the present time impurities are removed from molten pig iron, or thecomposition of alloys, when manufacturing pig iron, steel, and the like,are adjusted in blast furnaces, converters, open-hearth furnaces,electric furnaces, cupolas, etc. However, only a limited extent ofrefinement can be carried out with such conventional structures.

There has thus been a long-felt want in the art for an inexpensivepre-treatment or post-treatment of the molten metal to refine the latterin a manner which can be easily practiced and which can achieveconstant, predictable results.

Among the presently known methods for carrying out pretreatments, suchas desulfurization, are a ladle-transfer pouring method, the Pellanprocess, a method wherein a powdered desulfurizing agent such as carbideand the like is blown in with a gas in which the powder is suspended, anagitation method utilizing an impeller, and similar methods. All ofthese known methods have the serious disadvantage of being incapable ofachieving a constant rate of desulfurization, and in addition theysuffer from the disadvantage of an unavoidable loss of desulfurizingagent which does not react with the molten pig iron. This latter loss isexcessive due to spattering of the molten metal or insutficientagitation thereof, thus undesirably increasing the cost of thetreatment. Similiar difficulties and disadvantages are encountered in anunavoidable manner with known dephosphorization treatments as well as inknown treatments for adjusting the composition of alloys.

A more effective desulfurization method, according to which the ladle isvibrated, has been recently developed. With this latter method the ladleis vibrated so as to promote a more intimate contact between the moltenpig iron and the purifying agent, thus increasing the refiningefficiency. However, the cost of the vibrating installation and thepower required to vibrate a huge ladle and its contents is prohibitive,and in addition the ratio of the volume of 3,592,629 Patented July 13,1971 the molten pig iron to the volume of the ladle is small.Furthermore, this latter method is accompanied by the seriousdisadvantage of an unavoidable, excessive drop in the temperature of themolten pig iron.

Inasmuch as the refinement of molten metals such as molten irons or ironalloys is brought about by reactions between the slag and molten pigiron and reacting agents which are in a gaseous state, in order toaccelerate the reactions it is essential to increase the contact areabetween the treated metal which is in a liquid state and the reactingagent which is in a gaseous state, and the attempt is always to bringthe reaction agent which is in the gaseous state into contact withconstantly changing liquid surfaces of the molten metal which istreated. These factors are well recognized by those skilled in the art.Thus, in order to effectively utilize the reaction agents it isessential to provide a constant agitation of the reaction agents so asto cause them to come into intimate contact with the molten metal suchas molten pig iron. While a method such as the above ladle vibratingmethod achieves a certain degree of refinement, in a manner similar toother known methods, since the reaction agents are distributed over theentire surface of the molten pig iron the entire contents of the latterare stirred and it is necessary to vibrate or oscillate the huge ladlein its entirety in order to bring about the desired extent of contactbetween the treated metal and the purifying agent.

Thus, with the prior art techniques it has always been consideredessential to provide the largest possible area of contact between thepurifying agent and thus the entire mass of molten iron is stirred orotherwise agitated in order to attempt to achieve the intimate contactwith the purifying agent which will give the most satisfactory results.

SUMMARY OF THE INVENTION It is a primary object of the present inventionto provide a method for effectively refining molten metals whileavoiding the drawbacks of the prior art as referred to above.

Thus, it is an object of the invention to provide a method capable ofeffectively refining a molten metal in a simple, economical manner,utilizing a relatively small degree of agitation of the body of moltenmetal.

In accordance with the invention the molten metal which contains theimpurities and which is to be refined is poured into a vessel such as asuitable ladle, and a suitable purifying agent is added to react withthe molten metal so as to eliminate at least part of the impuritiesthereof. Then this molten metal to which the purifying agent has beenadded is stirred only in the region of the surface of the molten metal.The adding of the purifying agent to the molten metal and the stirringthereof is carried out during a period of time when parts of the body ofmolten metal within the vessel are still in motion.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way ofexample in the accompanying drawings which form part of this applicationand in which:

FIG. 1 is a sectional elevation of one possible embodiment of anapparatus for practicing the method of the present invention;

FIG. 2 is a top plan view of the structure of FIG. 1 with the ladlecover removed;

FIG. 3 is a schematic sectional elevation of a further embodiment of anapparatus for practicing the method of the invention;

FIG. 4 is a schematic sectional elevation of yet another embodiment ofan apparatus for practicing the method of the invention;

FIG. 5 is a graph illustrating the operation of the embodiment of FIG.4;

FIG. 6 is a schematic sectional elevation of yet another embodiment ofan apparatus for practicing the method of the invention;

FIG. 7 is a graphic illustration of one example of a method carried outaccording to the invention;

FIG. 8 is a graphic illustration of another specific example of a methodaccording to the invention;

FIG. 9 is a graphic illustration of the time during which parts of abody of molten metal remain in motion after the molten metal is pouredinto a vessel; and

FIG. 10 is a graph illustrating the results achieved in tests todetermine the relation between the depth of immersion of stirrers andthe number thereof.

DESCRIPTION OF PREFERRED EMBODIMENTS The invention is based upon theconcept or discovery that after a molten metal is poured into a vesselparts of the body of molten metal remain in motion over a substantialperiod of time. Thus, it has been found that due to natural convection,diffusion, and/or inertia of various parts of the molten metal, thereare within the body of molten metal currents which persist over asubstantial period of time after the metal is poured into a vessel.Thus, when a molten metal such as molten pig iron is poured into a ladlefrom a blast furnace, or is transferred to a vessel such as a torpedocar to be used in connection with charging an open-hearth furnace orconverter, or when the molten pig iron is situated within the front partof a cupola or in a trough which forms a runner from a blast furnace,flowing movements of parts of the body of molten metal within thevessel, in the form of currents of the molten metal, persist for aconsiderable period of time after the metal has been poured.

In order to establish these facts, experiments were carried out. Inthese experiments molten pig iron was poured into a ton ladle from ablast furnace, and an isotope of gold Au 128 was placed in the bottom ofthe ladle. The relationship between the elapsed time and the intensityof radiation emanating from the surface of the molten pig iron wasmeasured to obtain the results which are illustrated in FIG. 9. Thecurve D of FIG. 9 shows the results of measurements obtained when Au 128was incorporated into the molten metal 16 minutes after the pouringthereof into the ladle. The curve E of FIG. 9 shows the results obtainedwith measurements taken in a test where Au 128 was incorporated into theladle 39 minutes after the molten pig iron was poured. The curve F showsmeasurements taken when Au 128 was incorporated into the body of moltenmetal minutes after the pouring thereof into the ladle. From thesecurves it has been discovered that indeed a molten metal such as moltenpig iron, after it is poured into a vessel such as a suitable ladle,continues to have parts of the body of molten metal which persist inmotion over a very long period of time which in the case of pig iron hasa duration of at least one hour. Furthermore, the curves demonstratethat the molten metal such as molten pig iron mixes with the additive atan extremenly high speed.

Based upon the results of these tests, it has been concluded thatsufficient refining, such as desulfurization, can be carried out bytaking advantage of the fact that parts of the body of molten metal,after it is poured into a vessel, persist in motion over a long periodof time so that it is in fact unnecessary to stir the molten metalthroughout the body thereof and instead the stirring can be limited onlyto a relatively shallow portion of the molten metal in the region of itssurface where the molten metal is in contact with the purifying agent.It thus becomes unnecessary to carry out the stirring all the way downto the bottom of the vessel, as long as the refining operations arecarried out after the pouring during the period of time when parts ofthe body of molten metal persist in their flowing movements.

In the case of the desulfurization of pig iron extensive experimentshave demonstrated that 90% desulfurization can be achieved when moltenpig iron which has been poured into the ladle is stirred with a stirringmeans which has stirrer rods which extend into the body of molten metaldownwardly from the surface thereof to a depth which is less than V3 ofthe total depth of the molten metal. In this case desulfurization of8590% was achieved with the stirrer rods extending into the body ofmolten metal downwardly below the surface thereof to a depth of aboutVin to j of the total depth of the molten pig iron in the ladle.

FIG. 10 is a graph illustrating the results achieved duringdesulfurization on the one hand with a single stirrer rod inserted to adepth of l0-30% of the total depth of the molten metal and on the otherhand with three stirrer rods also inserted to a depth of l0-30% of thetotal depth of the molten metal. Thus, the lower curve of FIG. 10illustrates stirring with a single stirrer, while the upper curveillustrates stirring with three stirrers, and it is appaent from FIG. 10in both cases a relatively high degree of desulfurization was achievedeven though the stirring operations were limited to the region of thesurface of the molten metal.

In carrying out the tests used to provide the graph shown in FIG. 10,the molten pig iron was poured into a ladle having a capacity of 30 tonsup to a depth of 2000 mm. within the vessel, and CaC was added at a rateof 4 kg./THM. The stirring rods were rotated at rpm. It was found thatwhere the stirrer rods have an irregular cross section, such as a crosssection of X- shaped or Y-shaped configuration, a somewhat betterdesulfurization was achieved than in the case where stirrer rods ofcircular cross section were used, and in addition it was found that adepth of immersion of the stirrer rods less than As of the total depthof the molten pig iron was suflicient to achieve the desired results.

Thus. with the invention it is possible, by incorporating a purifyingagent such as a desulfurizing agent or a dephosphorizing agent into themolten pig iron after it is poured into a ladle or similar vessel andwhile currents persist in the body of molten metal to bring about thedesired degree of refining while stirring only a relatively shallowportion of the molten pig iron in the region of the surface thereof byway of a suitable stirring means. Thus, the desired degree ofdesulfurization or dephosphorization, in the case of molten pig iron,can be achieved without stirring the body of molten metal all the waydown to the lowermost part thereof in the vessel. It is only necessaryto stir the molten pig iron in the region of its surface, so that itbecomes possible to use a stirring means of simple construction, thusreducing the cost of the installation as well as the cost of the powerrequired to operate the stirring installation.

FIGS. 1 and 2 illustrate one possible embodiment of an apparatus forpracticing the method of the invention. With this embodiment there arefour stirrers in the form of elongated vertically extending rods 5 ofX-shaped cross section. These rods are fixed at their top ends to thelower surface of a horizontal disc 4 which thus fixedly carries thestirrers 5. These stirrers extend perpendicularly to the surface of thebody of molten metal in the vessel 1 downwardly into the molten metalonly to a depth which is in the region of the surface thereof, thisdepth being less than one third of the total depth of the body of moltenmetal. Thus, there is shown in FIG. 1 a body of molten pig iron 2 whichis to be refined by way of a purifying agent 3 which floats on thesurface of the molten pig iron and which is added after the molten pigiron is introduced into the vessel 1, which may take the form of aladle, although it may also be in the form of the runner of a blastfurnace or the front lower part of a cupola where the molten metal isaccessible, as is well known. The stirrer-carrying disc 4 is driven byan eccentric drive which forms part of the stirring means of thisembodiment and which includes the bevel gear train 8. This gear traindrives a disc which is eccentrically and pivotally connected to a cornerportion of an eccentric driving disc which is of substantiallytriangular configuration, as is apparent from FIG. 2. The discs whichare respectively pivotally and eccentrically connected to the corners ofthe plate 7 are supported for rotary motion about their axes,respectively, which extend vertically, in any suitable bearings, so thatthese relatively small circular discs support the eccentric plate 7 foreccentric rotary motion, and only one of these circular discs need bedriven by way of the drive 8 as, illustrated. A central portion of thetriangular eccentric camming plate 7 fixedly carries a shaft 6 whichextends vertically down to the top of the stirrer-carrying disc 4, thisshaft 6 being fixed to a central part of the disc 4 as well as to acentral part of the plate 7. Thus, with this construction the stirrers Swill be driven eccentrically along closed paths, bringing about stirringof the molten metal in the region of the surface thereof. Of course,these operations, as well as the addition of the purifying agent 3, arecarried out after the pouring of the molten pig iron 2 into the vessel 1while parts of the body of molten metal in the vessel 1 continue inmotion.

While the stirrers 5 of FIGS. 1 and 2 are shown as having an X-shapedcross section, other cross-sectional configurations can be used such asY-shaped, square, triangular, or even circular cross-sectionalconfigurations, although the irregular configurations provide superiorresults, as pointed out above.

The vessel 1 is covered by a lid which is indicated schematically inFIG. 1 and which is omitted from FIG. 2 so as to illustrate more clearlythe stirring means. This lid has a downwardly extending side wallengaging the exterior upper portion of the vessel and a top wall formedwith an opening large enough to accommodate the eccentric movement ofthe shaft 6. In addition, suitable tubes 10 extend through the sidewalls of the lid to the space beneath the latter to introduce a suitableprotective or atmospheric gas into the vessel Over the contents thereof.In the case of desulfurizing molten pig iron, the purifying agent iscarbide, calcium nitride, soda ash, and the like, while reducing gassuch as coke furnace gas, blast furnace gas, etc., are used as theatmospheric, protective gas forming the atmosphere above the contents ofthe vessel during the purifying reactions. In order to bring aboutdephosphorization of the molten pig iron, the purifying agents are ahighly basic sintered ore, limestone, and the like, while the protectiveatmosphere introduced through the tubes 10 is oxygen, as is well known.

The apparatus for practicing the method of the invention which thusrequires the plurality of elongated stirrers to be moved only in theregion of the surface of the molten body of metal is far simpler inconstruction and requires far less power than conventional structures ofthis type.

The material which is used for the stirrers 5 is refractory so as toprevent erosion thereof and so as to have no influence 0n the refiningreactions. For example, in the case of desulfurization of molten pigiron, reducing materials such as refractory materials of graphite areadvantageously used for the stirrers, particularly since they have ahigh thermal resistance and will remain uninfluenced by heat shock. Inthe case of dephosphorization of molten pig iron, since the stirrers arein contact with a highly basic slag, the stirrers are made of a basicrefractory material such as magnesia dolomite. However, inasmuch asthese latter materials do not have a particularly high thermalresistance and may indeed be influenced by heat shock, it is preferredto reinforce the stirrers by surrounding them with graphite-typematerials, such as those materials of the rods which are used in thecase of desulfurization of the pig iron. Thus, in this case, namely inthe case of dephosphorization, the stirrers which are made of abasically refractory material such as magnesia dolomite are covered withcoatings of a graphite-type of material.

According to the embodiment of the apparatus for practicing the methodof the invention which is illustrated in FIG. 3, the stirrer of thestirring means takes the form of a hollow cylindrical member 13 whoseaxis extends vertically, and a lower end portion of this cylindricalhollow stirrer is vertically immersed into the body of molten pig iron12 only to a depth which is situated in the region of the surfacethereof, this molten pig iron 12 having been poured into the vessel 11.Within the hollow stirrer 13 is situated at least part of the purifyingagent 3 which floats on the upper surface of the molten pig iron 12. Thecylindrical stirrer 13 is fixedly connected to a flange which issituated at the bottom end of a hollow shaft 15 which is eccentricallydriven as through a drive similar to that of FIGS. 1 and 2. Thus, thisdrive includes the eccentric camming plate 16 which may be similar tothe plate 7 and the bevel gear drive 17 which drives one of the rotarydiscs which is pivotally connected with a corner portion of the plate 16at a location spaced from the center of the disc which is driven by thebevel gear drive 17.

A suitable protective gas is supplied to the interior of the cylinder 13through a pipe 18 so as to control the gaseous phase or protectiveatmosphere within the cylinder 13. For example, in order to bring aboutdesulfurization, a reducing gas such as coke furnace gas or the like, isadmitted through the pipe 18, while in the case of dephosphorizationoxygen is supplied at a suitable pressure.

With this embodiment the upper surface of the molten pig iron which issituated outwardly beyond the cylindrical stirrer 13 is heated bycombustion of suitable gases introduced into the interior of the lid 19through the pipes 20. This lid 19 has a construction similar to the lidof FIG. 1 and is also provided in its top wall with an opening largeenough to accommodate the required extent of eccentric movement of thehollow shaft 15, and of course the pipe 18 moves with the hollow shaft15, this pipe 18 having a flexible, hose-type of connection with thesource of protective gas.

In a further embodiment of the invention which is illustrated in FIG. 4the stirring of the body of molten metal is brought about by way of asingle elongated stirrer 13a which may have an X-shaped cross section,or an eliptical cross section, if desired. With this embodiment thesingle stirrer is introduced through the opening in the lid into thebody of molten metal on which the purifying agent floats to a depthwhich is limited to the region of the surface of the body of moltenmetal, and through a drive such as the gear transmission 21 illustratedin FIG. 4 the single elongated stirrer 13a is simply rotated about itsaxis, any suitable bearing structure being provided to support thestirrer for rotary movement about its axis. Thus, in this case thestirrer does not extend perpendicularly to the surface of the moltenmetal but is rather inclined thereto at an angle other than a rightangle.

The stirring effect which is achieved with the embodiment of FIG. 4 isdetermined by the angle of inclination of the elongated stirrer and thespeed at which it is rotated. The curves of FIG. 5 illustrate therelation between the angle of inclination of the stirrer and the numberof revolutions thereof. Curve A shows the results achieved at variousangles of inclination when the stirrer is rotated at a high speed, whilethe curve B shows the results achieved at different angles ofinclination when the stirrer is rotated at an intermediate speed, andcurve C shows the stirrer effects achieved at different inclinations ofthe stirrer when the latter is rotated at a low speed.

In connection with FIG. 5, the high, intermediate and low speeds are,respectively, 130 r.p.m., 110 r.p.m., and r.p.m. In connection withExamples 1, 3, and 4, set

forth below, the depth of immersion of the stirrers were within a rangeof about 200 mm. to 250 mm.

Referring now to FIG. 6, the embodiment of the apparatus for practicingthe method of the invention which is illustrated therein includes avessel such as the ladle 26 in which the body of molten metal 27, suchas pig iron, is located. The vessel 26 is carried on a base member whichfixedly carries the upwardly directed standards or columns and 25' whichare fixed to each other at their top ends by an upper beam which carriesat its underside suitable brackets on which pulleys and 30 are supportedfor rotary movement. A beam 29 extends horizontally between thestandards 25 and 2S and is formed with openings or notches through whichthe standards extend, this beam 29 fixedly carrying at its undersideblocks 33 and 33' which slidably engage the columns 25 and 25'. Cables,ropes, or the like 30 and 31 are fixed to the outer ends of the beam 29,beyond the columns 25 and 25' and extend respectively around the pulleys30 and 30, so that these cables may be actuated to raise and lower thebeam 29. Instead of a cable-and-pulley system for raising and loweringthe beam 29, structures such as hydraulic jacks may be used.

The beam 29 carries an electric motor 32, connected to any suitablesource of current, and this motor through a suitable transmission drivesthe crank shaft 34 which is supported for rotation in suitable bearing.blocks 35 and 35 which are fixed to and extend upwardly from the beam29. At its intermediate crank portion, the crank shaft 34 is pivotallyconnected to a connecting rod 37 which is in turn pivotally connected at38 with the top end of a vertically displaceable plunger 36 whose axiscoincides with the central axis of the ladle 26, if desired. The beam 29is formed with a suitable opening carrying a bushing or the like throughwhich the plunger 36 is guided for vertical reciprocating movement. Thelower end of the plunger 36 is pivotally connected at 40 and 40' with apair of bell cranks 39 and 39', respectively, which are in turnpivotally connected at the intersections of their arms to supportingbrackets 41 and 41 fixed to and extending downwardly from the beam 29.Pivotal connections 42 and 42' are provided for the bell cranks 39 and39 at the brackets 41 and 41, respectively. The lower ends of the bellcranks 39 and 39' are respectively fixed to the top ends of a pair ofelongated stirrers 28 and 28 so that these stirrers, which may have anX- shaped cross section, respectively form extensions of the arms of thebell cranks which extend downwardly from the pivots 42 and 42,respectively.

Thus, with this embodiment the stirrer means includes the crank drivewhich produces oscillatory swinging movement of the stirrers 28 and 28'back and forth about the pivots 42 and 42', and these stirrers 2S and28' are symmeans acts only at the region of the surface of the moltenmetal such as molten pig iron, so that the cost of the apparatus and thecost for operating the same is relatively low, while at the same time ahighly efiicient refining can be achieved even though the stirring islimited to the region of the surface of the body of molten metal.Moreover, the protective atmosphere in which the refining actions takeplace can be readily controlled because the refining reactions takeplace only at the region of the surface of the molten metal. Inaddition, full utilization is made of the purifying agent since there issubstantiallv no loss thereof resulting from spattering or resultingfrom excessive amounts of purifying agent which do not enter into thereaction.

It is to be noted that the entire agitating action with the inventionresults solely from the movements within the body of molten metal whichstill persist plus the move ments derived from the stirring action, withthis action being not only limited to the region of the surface of themolten metal but also a stirring action difierent from simple rotarymovement of a stirrer about its own axis with the latter extendingperpendicularly to the surface of the molten metal. Thus, in all casesexcept that illustrated in FIG. 4 the stirrers move bodily with respectto the vessel so that they have a motion according to which they aredisplaced in their entirety with respect to the vessel which containsthe molten metal. In the case of FIG. 4, while the stirrer rotates aboutits own axis, this axis is not perpendicular to the surface of the bodyof molten metal so that the flat portions of the stirrer have verticalcomponents of movement, rather than solely horizontal components ofmovement, resulting in a stirring action beyond that which would beachieved if the stirrer was simply rotated about its own axis with thelatter axis extending perpendicularly to the surface of the moltenmetal.

The following are examples of desulfurization and dephosphorization ofruns of molten pig iron provided in connection with the manufacture ofsteel. The molten pig iron is poured into a ladle in accordance with themethod of the invention. The ladle has in these examples an internaldiameter of 1800 mm., a depth of 2000 mm., and contains the molten pigiron which is in the vessel at a depth of 1800 mm. The charge in theladle at each run for each example was 30 tons of molten pig iron.

Example 1 Desulfurization tests were carried outwith an apparatus havingthe construction shown in FIG. 1. The elongated stirrers had a length of1000 mm., and three stirrers were used while an eccentric motion wasimparted thereto. This eccentric motion had an eccentricity of mm. Theresults of the test runs are indicated in Table 1.

TABLE 1.RUN NO. 1

Concentration of S, percent Percent of Periods of Before Aftertlesullurtreatment,

Desullurizing agent (kg) treatment treatment jzing R.p.1n. min.

Carbide 8 0. 045 0. 009 80 10 Carbide 16 0, 032 0.003 01 120 10 Calciumnitride 1U 0. 028 0.003 80 15 metrically situated with respect to theaxis of the vessel Example 2 26. It will be noted that in accordancewith the invention the stirrers 28 also extend to only a small extentinto the body of molten metal beneath the surface thereof so that thestirring is limited to the region of the surface of the body of moltenmetal.

Similar desulfurizing tests were made with the apparatus illustrated inFIG. 4. In this case the length of the stirrer was also 1000 mm., and ofcourse only one stirrer was used. The depth of immersion was 200250 mm.Re-

Thus, with the method of the invention the stirring 7 sults of thesetests are shown in Table 2.

C oncentration of sulfur, percent Percent of Angle of Period BeforeAfter desulfurinclination, treatment,

Desulfurizlng agent tkg.) treatment treatmentization Rpm, degrees min.

Carbide 8 0. 042 0. 010 76 95 25 10 Carbide 10 I 0. 036 0, 004 80 100 10Calcium nitride 20 0. 034 0. 003 82 100 15 Example 3 to which thelocation of the entire stirrer with respect to Dephosphorization testswere carried out with the stirring apparatus shown in FIG. 3. Thestirrer was rotated at 110 r.p.m., and the dephosphorizing agent wasquick lime and a highly basic sintered ore (having a composition of FeO50%, Fe O 42.7%, SiO 3.5%, CaO 41.7% and CaO/SiO 11.9%). Oxygen wasejected through a lance opening into the hollow cylindrical stirrer. Theresults obtained were plotted on a graph to provide the curves shown inFIG. 7.

Example 4 The results of dephosphorizing runs using the apparatus shownin FIG. 4 were plotted in a graph to provide the curves of FIG. 8. Theangle of inclination of the stirrer was 20 with respect to a verticalline, and the stirrer was rotated at a speed of 130 r.p.m. while oxygenwas admitted to the space beneath the lid through a suitable lance.

While in the above examples reference is made to desulfurization anddephosphorization of molten pig iron, the invention can equally well beapplied to the refining of other molten metals such as iron alloys, andin addition it can be used for adjusting the composition of metal alloyssuch as iron alloys.

What is claimed is:

1. In a method of refining a molten metal which contains impurities, thesteps of pouring the molten metal into a vessel, to provide therein abody of molten metal, parts of which are in motion due to the pouring ofthe molten metal, adding to the molten metal a purifying agent whichreacts therewith to eliminate at least part of the impurities therefrom,and stirring the molten metal, to which the purifying agent has beenadded, only in the region of the surface of the molten metal, said stepsof adding the purifying agent and stirring the molten metal beingperformed after the metal is poured into the vessel during a period oftime when the parts of the body of molten metal within the vessel arestill in motion, due to the pouring of the molten metal, and the entirerelative movement between the purifying agent and the molten metal beingderived solely from the movement of the parts of the body of moltenmetal and the stirring action, said stirring action being carried outwith at least one stirrer extending into the molten metal only to adepth of 10-30% of the total depth thereof with the stirrer having abodily movement with respect to the vessel according the vesselcontinuously changes.

2. In a method as recited in claim 1, said metal being molten pig ironand said period of time having a duration of at least one hour.

3. In a method as recited in claim 1, said metal being molten pig ironand said purifying agent being a desulfurizing agent.

4. In a method as recited in claim 1, said metal being molten pig ironand said purifying agent being a dephosphorizing agent.

5. In a method as recited in claim 1, said step of stirring the moltenmetal being carried out with stirrers which extend into the molten metalperpendicularly to the surface thereof and which carry out eccentricmovements with respect to the vessel according to which the stirrers aredisplaced in their entirety along a given closed path with respect tothe vessel.

6. In a method as recited in claim 5 and wherein said stirrers swingtoward and away from each other respectively about horizontal axes.

7. In a method as recited in claim 1 and wherein said stirrer carriesout an eccentric movement with respect to the vessel and is in the formitself of a hollow enclosure to which the purifying agent is confined.

References Cited UNITED STATES PATENTS 2,319,402 5/1943 Heller 266343,392,009 7/1968 Holmes -59 3,459,536 8/1969 Touzalin 75-45 3,334,9938/1967 Nojima 75-45 2,290,961 7/1942 Heuer 7549X 2,397,737 4/1946 Heuer75-55 3,278,295 10/1966 Ostberg 7561 FOREIGN PATENTS 684,048 12/1952Great Britain 7593 242,012 1/1963 Australia 7561 L. DEWAYNE RUTLEDGE,Primary Examiner J. E. LEGRU, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE Certificate Patent No. 3,592,629 PatentedJuly 13, 1971 Ryo Ando, Tsutomu Fukushima, Eiichi Hiraguchi, and KokichiHagiwara Application having been made by Ryo Ando, Tsutomu Fukushiina,Eiichi Hiraguchi, and Kokichi Hagiwara, the inventors named in thepatent above identified, and Nippon Kokan Kabushiki Kaisha, Tokyo, Japen, a corporation of Japan, the assignee,

for the issuance of a certlficate under the PIOVISIOHS of Title 35,Section 256, of the United States Code, deleting the names of KokichiHagiwam and Eiichi Hiraguchi as joint inventors, and a, showing andproof of facts satisfying the requirements of the said section havingbeen submitted, it is this 23rd day of May 1972, certified that thenames of the said Kokichi Hagiwara and Eiichi Hiraguchi are herebydeleted from the said FRED W. SHERLING Associate Solicitor.

